The invention relates to air or gas distribution systems generally. More specifically the invention is concerned with distribution of air or other gas to a system of liquid-containing tanks, wherein the gas is to be bubbled up through liquid contained in the tanks, as in the case of a sewage treatment plant.
U.S. Pat. Nos. 4,720,360 and 4,863,644, owned by Enviroquip, Inc., disclose air or gas distribution structures primarily for use in waste water treatment plants, for aeration of the waste water being treated. The apparatus disclosed in the patents is intended to promote even distribution of gas among injection pipes, to produce small diameter gas bubbles for wide distribution in the liquid and to prevent clogging of gas orifices.
U.S. Pat. No. 5,325,646 of Hallsten Corporation discloses a tank or channel cover structure wherein one or more extruded structural members, tubular in cross section, support a flat, arched or domed cover from the edges of a tank or channel. The cover structures disclosed in the patent are adaptable for many purposes, including sewage treatment plants.
Previously, sewage treatment plants have required a network of pipes for distribution of air used in aeration of the sewage sludge contained in tanks. Such piping might be run along the surface at the exterior of a tank or sludge channel, with a series of branch pipes emerging from a main distribution pipe, in order to serve the entire area of the tank or tanks. Such a network of piping has been difficult to control as to even distribution of air or gas through the many downwardly extending bubbler pipes with gas orifices, and an orifice has typically been included on each gas bubbler pipe as a flow controller so that the system can be manually balanced as closely as possible by use of various orifice sizes. Typically these orifices have been beneath the surface, making them subject to clogging and difficult to access and making balanced distribution nearly impossible. In addition, some sewage treatment tanks of this nature are now required to be covered rather than open to the air as in the past. The covering of these tanks is complicated by the network of pipes, and accommodation must be made for these pipes.
It has been known prior to this invention to utilize foot bridge structure over an open sewage treatment tank as part of the air distribution means leading to drop pipes and bubblers. However, many different considerations, and also different structures, are involved in the case where a tank cover is provided to substantially totally seal the tank's interior from the atmosphere.
It is an object of this invention to utilize tank or channel cover structure such as disclosed in the above referenced U.S. Pat. No. 5,325,646 as not only structure covering a tank but also as a means or instrumentation for carrying the air or other gas to be distributed to various bubbler devices throughout the tank; and to employ diffuser structure of the type disclosed in U.S. Pat. Nos. 4,720,360 and 4,863,644. Thus, the invention uses the structure of U.S. Pat. No. 5,325,646 for two purposes simultaneously, therefore avoiding a network of pipes which would normally be provided to reach each vertical bubbler device and establishing an efficient system of built-in air channels for distribution of the gases, while allowing a closed and sealed tank system to have all bubblers/diffusers and orifices accessible from above the tank cover.